On Thu, 21 Apr 2005 14:45:21 -0600, Sylvan Butler
>> On Sat, 16 Apr 2005 12:34:26 -0600, Sylvan Butler
>>> For temperature, use Dallas/Maxim DS1820 temperature sensors. They are
>
>> Got it. Once we're in, I can graph with MRTG and handle the logic there.
>
> Yup. Project called One-Wire Weather (OWW), I think Simon has it on
> sourceforge now, might be an interesting reference or starting point. I
> think he sticks uses rrdtool to store and graph the data.
Excellent. Now we're _really_ in my area of comfort.
>> Any problem mixing low and high voltage wiring in the same box?
> Problem for me? No... And my understanding of the NEC (my only
> reference is a version or two out of date though) says that they are
> allowed to mix if the only reason is for control/sensing of the load and
> they only come together in the box where they actually need to be
> together. In other words, if you were going to switch a 120vac light
> with a low-voltage signal, the signal conductors and power conductors
> would have to be run seperatly, even if that required two conduit runs,
> until reaching the box where the load is controlled.
Gotcha. No other way to do that, is there. I think where I got messed
up on that was with putting a TV cable into the same box as the AC. (guys?
If it's not to code, please don't sell faceplates that give me that option,
ok?)
> Oh, and most SSRs are opto-isolated between control input and load
> terminals.
Right. I played with them back in the early 1980's, but not since. I had
a BBS running on a TRS-80 Color Computer, with code that a friend and I wrote
in BASIC. Due to the primative modem software, if someone could cause an
error to occur (or a disk error, or whatever), they'd get dumped to the
command line. This would have been bad, so I ran the modem power through
an SSR, which was powered through the reed relay on the computer's
main board. That reed relay would shut off at any error that basic
encountered. It was _intended_ to be the tape recorder's motor control
relay (so the tape would stop playing when you got a read error), but it
worked nicely to power the modem. When I started up the BBS, a command of
motor on
would turn on the relay, powering the SSR, turning on the modem. Any error
would shut it down and let me figure out what happened on the system to
make it error. Fun times. Kind of a brute-force firewall I guess.
>> Might even be able to use a laptop for it, I think I have a PII lying around
> Laptops usually work fine, but many times laptops only have 3v logic on
> the parallel port. So if your SSR is fussy, or the distance is long,
> you might need some buffering to get back to TTL levels (perhaps a 74hct
> series with schmitt-trigger inputs).
I'm comfortable in the 74ls world, so 74hct should be an easy transition.
Got a bunch of 74ls stuff that I'd been meaning to ebay, but maybe I can
use some of it. (who am I kidding...what I have, is what I won't need).
>> well-light my shop, and it's immensely better. Forget how we got on
>> the topic, but whatever - 12 4-tube light fixtures later, and it's great.
>
> Sounds nice, congratulations!
Thanks again
Dave
> One of the heat systems in my house is electric powered hydronic heat.
> I'm using a water heater, which is sufficient for my needs. Time-of-use
> electricity makes it cheaper than propane, nights and weekends.
>
> I'd like to do something a bit more sophisticated than my current
> control system, which is a day/hour timer switch. Can anyone suggest
> something which ideally would be:
>
> 1. Computer controlled (PC is OK, others are OK too)
> 2. Capable of driving a 30A 240VAC relay
> 3. Capable of taking temperature readings from several inputs
> to determine if the relay needs to be on or off
> 4. Reasonable cost
>
> Basically, a smart controller that knows about time and return water
> temperature, and turns on the heat when it's got access to cheap
> electricity and when the floor is cool enough to need it.
>
> Suggestions of vendors, or specific products, or even homebrew solutions
> are most welcome.
>
> Dave Hinz
>
Well relays are really "Old School" these days, you might think of using
SolidState Relays with Logic level inputs. I see some in Jameco that
will do 40Amps at 240Vac for around $20US. These can be driven from
Cmos drivers at logic levels. You also might look at the Opto22 stuff
that can be setup as a Network Device, on TCP/IP or ModBuss, or as a
Parallel Port device from a PC. I have used Dallas Semiconductor
Temp Sensers that come in TO92 cases and are Logoc Level devices for
doing liquid Temp monitoring. You would need an A/D of 8 bits or more
but they are dirt cheap.
Bruce in alaska
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>>> For temperature, use Dallas/Maxim DS1820 temperature sensors. They are
>
>> Got it. Once we're in, I can graph with MRTG and handle the logic there.
>
> Yup. Project called One-Wire Weather (OWW), I think Simon has it on
> sourceforge now, might be an interesting reference or starting point. I
> think he sticks uses rrdtool to store and graph the data.